AM receivers are utilized in numerous applications and are desirable for utilization in low power, small size applications, such as in portable command receivers. To obtain the desired sensitivity, most conventional AM receivers are of a superhetrodyne design or are based upon the superhetrodyne design. The superhetrodyne design produces the desired operating characteristics, but at the cost of relatively large size components and high power requirements which result in a large size receiver unit. This essentially precludes the superhetrodyne design from utilization in small size and/or low power applications.
Applicant researched the available receiver designs with a desired goal of designing a low power, small size AM receiver. In doing this research, applicant discovered some publications by Vasil Uzunoglu, such as The Synchronous Oscillator: A Synchronization and Tracking Network, IEEE JOURNAL OF SOLID-STATE CIRCUITS, Vol. SC-20, No. 6, December, 1985, directed to a synchronous oscillator for use in clock recovery systems. Applicant analyzed the circuit and surmised that the circuit must be operating to also demodulate the tracked signal. Applicant then built a test circuit to simulate what Applicant thought must be the active demodulating node. The test circuit initially appeared not to work or not to produce the surmised demodulated signal. Applicant, after further analysis, again concluded that the circuit must be producing a demodulated signal. Applicant again modulated the input of the test circuit with an RF signal, but additionally added a low pass filter coupled to the believed active node. The low pass filter revealed the presence of the demodulated signal, which resulted in the present invention. From reviewing the V. Uzonoglu articles, it is apparent that the demodulating capability of the synchronous oscillator was not discovered by V. Uzonoglu.
The present invention therefore was developed to solve the desirable goal of providing a small size, low power AM receiver.